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LM2623: Boost 2S AA Alkaline to 6V 400mA

Philipp Schaefer
Prodigy 10 points
Part Number: LM2623
Other Parts Discussed in Thread: LM2621

Hello,

for a current project I'm in need for a boost converter, that provides up to 400mA at 6V (normal operation <350mA). For input I have two alkaline AA cells in series. The minimum supported input voltage should therefore be close to 1.8V.

The device has to provide this current for a maximum of 20s and will be able to cool down afterwards for at least 40s. 

I calculated a peak current of 1.71A, which should be ok for the LM2623.

However looking at Figure 7 in the datasheet I am worried, that for the given parameters a stable output voltage can't be achieved.

My current schematic looks like this:

I also considered the LM2621 for this application and am happy to consider other devices if they fit my budget.

Thanks in advance for any advice.

Philipp Schaefer

  • 0
    TI__Guru 71675 points
    Your concern is a reasonable one, as you max load is just on the border line of current limit when Vin=1.8V. The datasheet curve was measured with 4.7uH inductor, and your 33uH can help you to pass higher load current under the same peak current limit. You should also use a 20V Schottky instead of the 40V one.

    Another option is the TPS55332, which has a higher current capability.